chap xii.] NERVOUS SYSTEM OF CHORDATA. 415 



incessantly preening, and, when feeding movements 

 are started, the chelate legs rob and play at cross pur- 

 poses with each other as well as four distinct indivi- 

 duals could do " ( J. Ward). 



This quotation will bring very forcibly to the 

 mind the value and meaning of gangl ionic masses in 

 the separate segments. 



So far as our present knowledge extends, we are 

 led to the belief that the spinal cord of the lower 

 Vertebrates (as represented by the frog) has much 

 greater independence than that of the higher, as re- 

 presented by the dog, or by man. For example, if 

 the brain of a frog be removed, the animal will still 

 execute movements, to which it is impossible to re- 

 fuse the name of purposeful ; in the Mammal, on 

 the other hand, the movements which, under similar 

 conditions, are similarly excited, are irregular and 

 without order. Extirpation of the cerebral hemi- 

 spheres of a Mammal results in death after a few 

 hours, while the frog may be kept alive for an indefi- 

 nite period, if suitable care be taken of it. 



The general functions of the various parts of the 

 brain have been discussed in the volume 011 "Human 

 Physiology" (chap. xiv.). 



The Cliordata are to be distinguished practically, 

 even if not morphologically, from the majority of the 

 so-called Invertebrata by the fact that the nervous cord 

 lies on the dorsal aspect of the body, and not on that 

 on which the mouth is situated ; at the same time 

 it is to be borne in mind that in the Nemertinea the 

 nerve cords often tend to lie dorsally. and that in 

 Peripatus the two cords are, at the hinder end of the 

 body connected together by a commissure which lies 

 above or dorsally to the terminal portion of the in- 

 testine. Similarly, there are certain points in the 

 anatomy of the vertebrate brain, too complicated to 

 be here described, which afford some evidence in 



